Plants Flashcards
What is rubisco?
a protein in leaves that fixes carbon in the Calvin Cycle
What are the unique features of plants?
cell walls, large vacuoles, chloroplasts, plasmodesmata, polyploidy, and self-fertilization (possible but not preferred)
Process of Making Transgenic Plants
- Ti plasmid
- Insert foreign DNA (transgene) into plasmid > recombinant plasmid
- Introduce into Agrobacterium tumefaciens bacteria
- Add Agrobacterium into petri dish of plant shoot apices
- Transform
- Transfer shoots into rooting medium
- Transfer to soil
Why does making transgenic plants work so well?
The infection with Agrobacterium is efficient and entire plants of many species can be regenerated from calli tissues which is totipotent
Examples of transgenic plants that improve nutritional traits
- rice that is rich in beta-carotene
- cassava that is enriched w/ protein, iron, beta-carotene, and NO cyanide
- edible cotton seeds (low levels of gossypol toxin)
Example of transgenic plants that improve the environmental adaptations of plants
tomatoes that are salt tolerant in salty soil
What are secondary metabolites?
-special chemicals that are not used for cellular metabolism
-may attract pollinators or repel/poison predators
-stored in vacuoles
Examples of secondary metabolites in plants
-morphine > poppy
-caffeine > coffee
-cocaine > cocoa plant
-nicotine > tobacco
What secondary metabolite is in willow tress?
salicylic acid
What is salicylic acid?
a defense molecule produced by willow trees and is similar to the active ingredient of aspirin
What is its role in willow trees?
-resistance to pathogens (viruses)
-a hormone to signal unexposed areas of a plant that an infection is underway
Plant Growth Hormones
-Abscisic acid (ABA)
-Auxins
-Brassinosteroids
-Cytokinins
-Ethylene
-Gibberellins
What is ethylene?
a gas that acts as a plant hormone, promotes leaf abscission and fruit ripening, causes an increase in its own production
What can you do to quicken ripening?
Add ethylene to storage chambers
What can you do to delay ripening?
Use ethylene scrubbers and absorbents that remove ethylene from the atmosphere in fruit storage chambers
Ethylene Triple Response
If stems pushing up through the soil encounter a stone, they release ethylene from their tips which:
1. slow stem elongation
2. thickens the stem to make it stronger
3. makes the stem grow horizontally
How can ethylene Triple Response be mimicked?
by treating plants w/ ethylene gas
What happens to ethylene insensitive mutants in the presence of ethylene?
they fail to undergo the Triple Response
What happens to constitutive triple response plants in the absence of of ethylene?
they undergo the Triple Response anyways
Ethylene signaling pathway (ethylene absent)
- ethylene receptors (ETR1) activate CTR1 protein kinase
- CTR1 protein kinase phosphorylates EIN2 and PREVENTS its cleavage
- In the nucleus, EBF1/2 proteins target TFs EIN3/EIL1 for ubiquitylation and degradation
- NO ethylene response
Ethylene signaling pathway (ethylene present)
- ligand-bound ethylene receptors no longer activate CTR1
- Proteolytic release of C-terminal end of EIN2
- Protein translation of EBF1/2 inhibited
- EBF1/2 levels decrease
- EIN3/EIL1 levels become stabilized
- This turns on extensive transcriptional cascade involving TF ERF1
- ETHYLENE RESPONSE
Are CTR components repressors or activators of the Triple Response?
repressors
Are EIN components necessary or unnecessary for the Triple Response?
necessary
What do auxins do?
They mediate many responses of plant shoots
-indoleacetic acid (IAA) = most important
What is phototropism?
The tendency for plants to grow toward light sources. A result of differential growth in the direction of the light.
Charles and Francis Darwin canary grass seedlings experiment
- When top mm of coleoptile of a grass plant is COVERED, the plant cannot respond to the direction of light
- Since photoreceptors are in the coleoptile, the bending takes place in the growing region below the tip
- A signal must pass from the tip to growing region
What growth hormone is diffused down a plant stem?
IAA in the coleoptile tip
Lateral redistribution of auxin in phototropism
- Light strike a coleoptile from one side
- Auxin moves to the shaded side
- Growth and cell elongation on that side is increased
- Seedling bends toward the light (shaded side wants to be near light)
Lateral redistribution in gravitropism
- Shoot tips over
- Heavy statolith organelles sink to the bottom of cells
- They use Ca2+ signaling to mediate transport of auxin to the lower side of the shoot
- This causes more rapid growth there
- Seedling bends upward
Auxin concentration in shoots vs. roots
shoots: higher conc. = more rapid growth
roots: higher conc. = slower growth in roots
Process of cell expansion
- Auxin causes release of protons and expansins from cytoplasm into cell wall space
- Expansins are activated by protons and modify H-bonding btwn polysaccharides in plant wall
- Turgor pressure pushes against wall
- If wall is loose, cell changes shape
- Microfibrils are deposited
What photoreceptor initiates phototropism?
a yellow pigmented protein: PHOTOTROPIN
Phototropin and phototropism
- Blue light is absorbed
- phototropin initiates a Ca2+ signal transduction pathway leading to auxin redistribution, H+ and expansin secretion
- differential growth > phototropic curvature
Mimosa plants
Sensitive to touch and will droop
Large fluid-filled vacuoles can rapidly lose water and make cell shrink > rapid branch movement
deMairan’s Experiment using Mimosa
daily rhythms of “sleep movements” of leaves are evidence for an endogenous biological clock in plants
1. Mimosa in window and in cabinet during day: leaves are upright
2. Mimosa in window and cabinet during night: leaves droop
Sporangium
an enclosed capsule that contains spores produced in fungi and many more species
Phloem
transport carbohydrates from sources to sinks through the sieve elements
Plasmodesmata
intercellular pores connecting adjacent plant cells allowing membrane and cytoplasmic continuity and are essential routes for intercellular trafficking, communication and signaling in plant development and defense
